How to Clean Optical Filters

How To, Learning Center

While the Iridian filters are hard coated filters, the filters are delicate and should be handled with care to avoid or minimize direct contact with any other optics. All Iridian filters may be cleaned using the following recommended method.


1) Many contaminants on the surface of the filters are loosely attached to the surface and can be removed by blowing off with N2. Hold the filter in one hand using laboratory gloves or finger cots.  Always use a gentle to moderate air flow and maintain an oblique angle and remember to begin the air stream while pointing away from the filter first, then slowing move the air stream over the filter surface at an angle.  Repeat this procedure on the other side of the filter.

2) If dust or debris remains, it must be removed with mechanical force and/or organic solvent. Create a firm, pointy tip with the Kimwipe in a triangular shape or wrapping it around a swab. Moisten the Kimwipe or swab with Methanol or Acetone, but avoid excess solvent. If the wipe or swab is fully saturated, it should be gently shaken or dabbed on a wipe to remove excess drops of solvent.  Use a new wipe or swab with each cleaning attempt.

Methanol and Acetone each have benefits and drawbacks. Generally, more active solvents (like acetone) attack a broader range of contaminants more quickly, but also evaporate more quickly than Methanol.  Acetone has excellent cleaning action but it dries very quickly and it thus leave behind residue on the surface. Methanol may require to wipe multiple times to remove all the contaminants but it dries slowly, reducing the risk of leaving a solvent residue on the surface of the filter.

It is recommended to maintain continuous motion at a constant speed, but do not apply pressure to the swab or wipe. It is also recommended to use the circle cleaning pattern starting from the center and goes onward to the outside of the filter. Each time the wiping motion comes to a stop, it is likely that residue will remain on the surface at that point, so maintain constant speed until the swab has moved off of the surface of the optic.

3) Use a bright light source to inspect the filter to ensure that it is clean. Simply tilt and rotate the filter while viewing it as close to your eye. If contamination remains, start with a brand new wipe or swab and repeat step 2 above.

4) Repeat steps 1 – 3 for the other side of the filter if contamination exists.

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